java泛型--概念、使用、自定义……

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0，泛型不能有用于static的。

1，Class

Class<Boolean> clazz 等效于 Boolean.class;

Class<T> valueType 等效于 T.class

public void _testGeneric(Class<?>clazz)

等效于

public <B> void _testGeneric(Class<? extends B>clazz){

2，通配符

?只能用于方法泛型，不能用于类泛型。

3，泛型就是不确定类型

//泛型如果为确定类型时，就没必要存在了，就想这个警告：//The type parameter Plant is hiding the type Plantpublic class Test2<Plant> {private Plant t;public Plant get(){return t;}}

4，把子类使用的其他具体类型传给父类，让父类统一处理。

例子：class Apple extends Fruit extends Plant implements Living

public class PlantFSM<T extends Plant> {private T owner;public PlantFSM(){}public PlantFSM(T owner){this.owner = owner;}public T getOwner() {return owner;}public void setOwner(T owner) {this.owner = owner;}}

public class AppleFSM extends PlantFSM<Apple> {public AppleFSM(){}public AppleFSM(Apple owner) {super(owner);}public static void main(String[] args) {AppleFSM appleFSM = new AppleFSM();Apple apple = new Apple();//自动为Apple类型：com.generic.PlantFSM.setOwner(Apple owner)appleFSM.setOwner(apple);//自动为Apple类型：Apple com.generic.PlantFSM.getOwner()appleFSM.getOwner();}//方法定义的泛型Fpublic <F> F getF(){return null;}}

反编译后

public class PlantFSM{    public PlantFSM(){}    public PlantFSM(Plant owner){        this.owner = owner;    }    public Plant getOwner(){        return owner;    }    public void setOwner(Plant owner){        this.owner = owner;    }    private Plant owner;}

public class AppleFSM extends PlantFSM{    public AppleFSM(){}    public AppleFSM(Apple owner){        super(owner);    }    public static void main(String args[]){        AppleFSM appleFSM = new AppleFSM();        Apple apple = new Apple();        appleFSM.setOwner(apple);        appleFSM.getOwner();    }    public Object getF(){        return null;    }}

5，

例子2

public interface IProcessor {public String process(String idipPacket);public int getReqCmdId();public int getRespCmdId();}

/** * <"B">与<"BODY">没任何区别，只是一个类型定义（占位符）。 * @author naijiang.wang */public abstract class AbstractProcessor<BODY> implements IProcessor{@Overridepublic String process(String json) {DataPacket<BODY> dataPacket = getDataPacket(json);response = response(dataPacket, serverId);Object response = null; try {dataPacket = getDataPacket(json);response = response(dataPacket, serverId);} catch (Exception e) {e.printStackTrace();}finally {if(response == null) {response = responseForResult(dataPacket.getHead(), ResultType.API_ERROR);}resp = JsonUtils.toJson(response);}return resp ;}//返回的泛型范围，可以大于真实具体的类型返回。比如：DataPacket.body是QueryReq类型。private DataPacket<BODY> getDataPacket(String json) {return JsonUtils.toBean(json, DataPacket.class, getRequestBodyClass());}public abstract Class<BODY> getRequestBodyClass();private DataPacket<?> response(DataPacket<BODY> dataPacket, Integer serverId) {DataPacket<?> response = process(dataPacket.getHead(), dataPacket.getBody(), serverId);return response;}//子类方法中body比如是：QueryReq类型。<?>表示不是BODY泛型public abstract DataPacket<?> process(DataHeader head, BODY body, Integer serverId);}

public class QueryProcessor extends AbstractProcessor<QueryReq>{@Overridepublic Class<QueryReq> getRequestBodyClass() {return QueryReq.class;}@Overridepublic DataPacket<?> process(DataHeader head, QueryReq body, Integer serverId) {QueryResp queryResp = new QueryResp();//填充数据return new DataPacket<QueryResp>(head, queryResp);}}

http://www.infoq.com/cn/articles/cf-java-generics

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